The present invention relates to semiconductor integrated devices and, more particularly, to effective technology to be utilized, for example, in a semiconductor integrated device for an echo canceler being provided in a subscriber line circuit of the ISDN: Integrated Service Digital Network.
There is an integrated service digital network which carries out data transmission using analog transmission lines for telephone subscriber lines. The integrated service network is provided with a subscriber line circuit corresponding to each subscriber line. In the subscriber line circuit, sending data are converted into analog sending signals and sent out from a hybrid circuit into the subscriber line, and analog receiving signals, being inputted from the subscriber line through the hybrid circuit, are recovered into receiving data. That is, the subscriber line is a so-called bidirectional transmission path, and analog sending signals corresponding to analog sending data and analog receiving signals corresponding to analog receiving data are found simultaneously on the subscriber line. Therefore, the subscriber line is provided with an echo canceler for removing reflected noises generated corresponding to the sending data, that is, echoes from the analog receiving signals being received and for extracting the receiving data, and a training mode for getting echo-removed data being subjected to operation processing in removing the echoes is prepared.
An echo canceler (echo canceling device) for digital transmission is disclosed, for example, in Japanese patent application laid-open No. 245734/1987.